In order to provide an alternative to petroleum based fuels, ethanol or a blend of gasoline and ethanol is increasingly being used to drive internal combustion engines of motor vehicles. So-called flex fuel vehicles, which can be driven with fuels containing ethanol in addition to gasoline, are particularly practical for the driver of a motor vehicle. The ethanol content of said fuels usually varies between 0% and 85%. The challenge, which thereby arises, is that the internal combustion engine is driven according to the prevailing fuel in use. It must thereby be taken into account that gasoline and ethanol have a different combustion behavior. That is why the ethanol content in the fuel has to be determined as exactly as possible in order for an optimal knock control, an ignition at the ideal point in time, an injection with the correct air/fuel mixture etc. to take place.
The following conventional methods are known from the technical field.
A known method provides for an ethanol content sensor to be used, which ascertains the ethanol content of the fuel present in a fuel tank and supplies a corresponding signal to the control system of the internal combustion engine.
Another method goes without this additional ethanol content sensor and instead uses the fact that the stoichiometric air requirement is a function of the ethanol content. Provision is thus made in this method for the closed-loop lambda control to be monitored after a filling of the tank (fueling) has been detected. The ethanol content of the fuel is then suggested as a function of the deviation of the closed-loop lambda control from a map-based pilot control.
A disadvantage of the technical field is that the method, which was first mentioned, requires an additional ethanol content sensor and that the second method depends upon the closed-loop lambda control not being disrupted by other influencing factors. It is, therefore, questionable whether a lambda deviation, which was detected in the closed-loop lambda control, can actually be attributed to an altered ethanol content in the fuel or whether in fact tolerances in the system or air conditions, which have changed, are responsible for the deviation in the closed-loop lambda control.